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排序方式: 共有813条查询结果,搜索用时 15 毫秒
51.
P. Thomas L. N. Sathapathy K. Dwarakanath K. B. R. Varma 《Bulletin of Materials Science》2007,30(6):567-570
CaCu3Ti4O12 (CCTO) was synthesized and sintered by microwave processing at 2·45 GHz, 1·1 kW. The optimum calcination temperature using
microwave heating was determined to be 950°C for 20 min to obtain cubic CCTO powders. The microwave processed powders were
sintered to 94% density at 1000°C/60 min. The microstructural studies carried out on these ceramics revealed the grain size
to be in the range 1–7 μm. The dielectric constants for the microwave sintered (1000°C/60 min) ceramics were found to vary
from 11000–7700 in the 100 Hz–00 kHz frequency range. Interestingly the dielectric loss had lower values than those sintered
by conventional sintering routes and decreases with increase in frequency. 相似文献
52.
Sudhir Varma 《International Journal of Pavement Engineering》2016,17(5):388-402
Appropriate characterisation of individual layer properties is crucial for mechanistic analysis of flexible pavements. Typically in inverse analyses, pavements are modelled as elastic or nonlinear elastic to obtain layer material properties through non-destructive falling weight deflectometer (FWD) testing. In this study, a layered viscoelastic–nonlinear forward model (called LAVAN) was used to develop a genetic algorithm-based backcalculation scheme (called BACKLAVAN). The LAVAN can consider both the viscoelastic behaviour of asphalt concrete (AC) layer and nonlinear elastic behaviour of unbound layers. The BACKLAVAN algorithm uses FWD load-response history at different test temperatures to backcalculate both the (damaged) E(t) and |E*| master curve of AC layers and the linear and nonlinear elastic moduli of unbound layers of in-service pavements. The BACKLAVAN algorithm was validated using two FWD tests run on a long-term pavement performance section. Comparison between the backcalculated and measured results indicates that it should be possible to infer linear viscoelastic properties of AC layer as well as nonlinear elastic properties of unbound layers from FWD tests. 相似文献
53.
Organic-inorganic polymers formed by hydrolysis/condensation reactions of alkoxide precursors, such as organically modified silanes (Ormosils) are used for several industrial applications such as electronic, optical and protective anticorrosion coatings. Such materials possess superior chemical stability, physical strength and scratch resistance characteristics when compared to organic polymers. Further performance improvement can be achieved through the incorporation of zirconium and titanium based nanoparticles, also formed through from precursors via the sol-gel process. However due to the inherent reactivity differences of the above precursors, they must be hydrolysed separately before being combined for final condensation. Zirconium precursors are commonly chelated using acetic acid or acetyl acetonate prior to hydrolysis, to lower the hydrolysis rate.In this body of work, 3,4-diaminobenzoic acid (DABA) and acetyl acetonate (acac) were compared as chelating ligands for controlling the hydrolysis reactions of zirconium n-propoxide to form nanoparticles within a silane sol matrix. The sols were applied as coatings on aerospace grade aluminium alloy AA 2024-T3 and characterised by physical, spectroscopical, microscopical, electrochemical and calorimetric techniques. The electrochemical properties of the coatings, as characterised by EIS and PDS, correlated with neutral salt spray evaluations confirming that the use of DABA as a chelating ligand significantly improved the coating performance when compared to the traditional diketone ligand. The data indicates the anticorrosion properties of the nitrogen rich chelate have a key role in protecting the alloy through the formation of smaller zirconium nanoparticles, thus improving the polymer network stability. 相似文献
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56.
S. K. Varma Erica Corral Erika Esquivel Daniel Salas 《Metallurgical and Materials Transactions A》1999,30(9):2539-2545
A solutionizing heat treatment of 2014 aluminum alloy reinforced with 0.15 volume fraction of alumina particles (VFAP) results
in deformation-induced precipitation during rolling and tensile deformation, with 0.10 VFAP, at room temperature. The extent
of precipitation increases with increase in time and/or temperature of solutionizing. An attempt has been made to identify
the various types of precipitates in the samples deformed to a given strain and in fractured conditions. The work-hardening
curves and tensile properties of the composites have been shown to be dependent on the time and temperature combination of
the solutionizing process. 相似文献
57.
In certain regions of operating conditions, chemical reactors may exhibit parametric sensitivity; i.e., small changes in one
or more of the reactor input parameters lead to much larger changes in the output variables. Since such behaviour leads to
deleterious performance, it is of practical interest to identify regions of parametric sensitivity in the reactor parameter
space. Until recently, this could be done only to describe thermal runaway, and only for those systems where a temperature
profile could be defined. Both of these limitations can be removed by consideringthe generalized criterion for parametric sensitivity, whereby sensitivity ofany output of the model toany input can be treated. Applications of the generalized criterion are discussed, with specific examples including pseudohomogeneous
and heterogeneous model tubular reactors, a nonisothermal CSTR, and a polymerization reactor.
Dedicated to Dr L K Doraiswamy — Gentleman, Scholar, Friend — on his sixtieth birthday. 相似文献
58.
59.
M. Deepa N. Sharma P. Varshney S. P. Varma S. A. Agnihotry 《Journal of Materials Science》2000,35(21):5313-5318
Peroxypolytungstic acid derivative (APTA) and peroxypolytungstic acid derivative coupled with a dicarboxylic acid additive i.e., oxalic acid dihydrate (APTA + OAD) in xerogel form, synthesized by a wet chemistry route were the solid sol-gel precursors for casting WO3 films. These bulk materials have a complex structure owing to the presence of several groups such as acetate, peroxy anions and water molecules in their basic matrix. Additionally, oxalate ions constitute an integral part of the structure in the APTA + OAD xerogel. Detailed FTIR analysis of these coordination compounds has thrown light on the modes of association of the various anions or groups with tungsten metal ion. The mode of coordination of the acetate ion as a bidentate as well as a monodentate ligand enabling chelate formation and the several other chemical linkages prevalent in APTA have been established. Upon the incorporation of OAD in APTA, the net ramifications are drastic changes in the structure inclusive of changes in the nature and strength of metal - ligand bonding, which is exemplified by FTIR studies of (APTA + OAD) xerogel. 相似文献
60.